Pressure around the choke valve

Problems: •The larger the difference between the inlet and outlet pressures, the higher the potential for damage to the internals of the choke. •When DP ratio (= DP/P1) rises above 0.6, damage is likely. Look at choke type, materials of construction, and deployment methods (multiple chokes needed in series )

Cavitation During Liquid Flow:

VENA Contracta Phenomenon:

The consequences of the low pressure region in the choke can lead to severe problems with cavitation and related flashing (vaporization).

Expansion of gas (and solutions containing gas) cools the surroundings. Excessive temp losses and presence of water vapor can form an ice plug and block flow.Expansion of gas (and solutions containing gas) cools the surroundings. Excessive temp losses and presence of water vapor can form an ice plug and block flow.

Choke Sizing •Cv = coefficient value –Number of gallons of water per minute that will pass through a restriction with a pressure drop of 1 psi at 60oF. –Used as the “flow capacity index”. –Does not correspond to a specific throttling method.

Erosion: Erosion – damage caused by impingement of particles, droplets, bubbles and even liquid on any solid surface at high velocity. To reduce erosion, slow down the velocity. A choke is required for throttling, never use a gate valve. If wells must be brought on line without a choke, use the outer wing valve if rated for the job. Erosion in a positive of bean choke from micron sized fines and high velocity gas flow.